冒泡排序：先拍第一个元素，经过一轮的循环
var a = [3,2,6,1]
for(let i =0;i<a.length;i++){
for(let j =0;j<a.length-i-1;j++){
if(a[j]>a[j+1]){
let tmp = a[j]
a[j] = a[j+1]
a[j+1] = tmp
}
}
}
console.log(a)
插入排序：拿出一个元素，和其他元素相比，依次比较
var a = [3,1,2,6]
for(let i=0;i<a.length;i++){
for(let j=i+1;j<a.length;j++){
if(a[i]>a[j]){
let tmp = a[i]
a[i] = a[j]
a[j] = tmp
}
}
}
快速排序：使用二分法概念，找出中间元素，左右两侧分别和他比较经过递归，获取最终的排序结果
function fastSort(arr){
if(arr.length<=1)return arr
let midIndex = arr.length/2;
//把原数组中中间元素剔除
let midVal = arr.splice(midIndex,1)[0]
let lefArray = []
let rightArr = []
for(let i = 0;i<arr.length;i++){
let item = arr[i];
item<midVal?lefArray.push(item):rightArr.push(item)
}
return fastSort(lefArray).concat(midVal,fastSort(rightArr))
}
同样的，我们也可使用es6提供的方法 arr.sort,直接实现排序
打乱顺序
function getL (list){
let arr = []
if(list.length>1){
for(let i=0;i<list.length;i++){
let left =list[i]
let a = [...list]
a.splice(i,1)
let pre = getL(a)
console.log(pre)
for(let i=0;i<pre.length;i++){
let tmp1 = [left,...pre[i]]
arr.push(tmp1)
}
}
} else {
arr.push(list)
}
return arr
}
promise简单实现
promise的all方法是只有全部成功才会进入，否则进入catch。race是第一个成功就进入then,否则进入catch
var pro1 = ()=>{
return new Promise((res,rej)=>{
res('pro12')
console.log('pro12')
})
}
var pro2 = ()=>{
return new Promise((res,rej)=>{
rej('pro23')
console.log('pro23')
})
}
var pro3 = ()=>{
return new Promise((res,rej)=>{
res('pro33')
console.log('pro33')
})
}
// pro12 pro23 pro23error
Promise.all([pro1(),pro2()]).then(res=>{console.log(res+"all res")}).catch(rej=>{console.log(rej+"error")})
// pro12 pro33 [pro12,pro33]
Promise.all([pro1(),pro3()]).then(res=>{console.log(res)}).catch(rej=>{console.log(rej+"error")})
// pro23 pro12 pro33 pro23race error
Promise.race([pro2(),pro1(),pro3()]).then(res=>{console.log(res+"race res")}).catch(rej=>{console.log(rej+"race error")})
// pro12 pro23 pro33 pro23race res
Promise.race([pro1(),pro2(),pro3()]).then(res=>{console.log(res+"race res")}).catch(rej=>{console.log(rej+"race error")})
const status=['pending,fulfilled','reject']
class Promise1{
constructor(callback){
this.status = status[0]
this.val = null //成功
this.res = null //失败
callback(this.resolve,this.reject)
this.resolveArr = [];
this.rejectArr = [];
}
resolve=(val)=>{
if(this.status===status[0]){
this.status = status[1]
this.val = val
this.resolveArr.forEach(fun=>fun(val))
}
}
reject=(val)=>{
if(this.status===status[0]){
this.status = status[2]
this.res = val
this.rejectArr.forEach(fun => fun(val))
}
}
then=(onFullFill,onReject)=>{
if(this.status === status[0]){
return new Promise1((resolve,reject)=>{
this.resolveArr.push(val=>{
try {
const result = onFullFill(val);
// 如果返回是promise的话 继续then方法
if(result instanceof Promise1){
result.then(resolve,reject)
} else {
resolve(result)
}
} catch (error) {
reject(error)
}
})
this.rejectArr.push(val=>{
try {
const result = onReject(val);
// 如果返回是promise的话 继续then方法
if(result instanceof Promise1){
result.then(resolve,reject)
} else {
resolve(result)
}
} catch (error) {
reject(error)
}
})
})
}
}
}
数组打乱顺序
function shuffle(arr){
let m = arr.length, t,i
while(m){
i = Math.floor(Math.random() * m--)
console.log(i)
t = arr[m]
arr[m] = arr[i];
arr[i] = t;
}
return arr
}
instanceof 实现
function ins(left,right){
let l = left.__proto__
let r = right.prototype
while(true){
if(l=== null) return false
if(l === right) return true
l = l.__proto__
}
}
寄生组合继承
function S(name){
this.name = name
}
function C(name){
S.call(this,name)
}
var b = Object.create(s.prototype)
C.prototype = b
b.constructor = C
bind 实现
Function.prototype.bind = function(ctx){
var arg =[...arguments].slice(1)
var that = this
return function(){
return that.apply(ctx,arg.concat(...arguments))
}
}
klh
function kla(){
var arg = [...arguments]
var add = function(){
arg.push(...arguments)
return add
}
add.toString = ()=>{
return arg.reduce((sum,item)=>sum+item)
}
return add()
}
new的过程
function ne(fn,...rest){
var a = new Object()
a.__proto__ = fn.prototype
var res = fn.apply(a,rest)
return res instanceof Object ?res :Object
}
重复子串的查找过程
var longestCommonSubsequence = function(text1, text2) {
const txt1Arr = text1.split("")
const txt2Arr = text2.split("")
const m = txt1Arr.length
const n = txt2Arr.length
const arr = Array(m+1).fill(0).map(item=>new Array(n+1).fill(0))
for(let i=1;i<=m;i++){
let txt1 = txt1Arr[i-1]
for(let j=1;j<=n;j++){
let txt2 = txt2Arr[j-1]
if(txt1 === txt2){
arr[i][j]=arr[i-1][j-1]+1
} else {
arr[i][j] = Math.max(arr[i-1][j],arr[i][j-1])
}
}
}
return arr[m][n]
};
深度优先遍历
function getCurList(list){
let arr = [], stack = [list]
while(stack.length!==0){
let tmp = stack.pop()
arr.push(tmp.value)
if(tmp.childRight){
stack.push(tmp.childRight)
}
if(tmp.childLeft){
stack.push(tmp.childLeft)
}
}
return arr
}
树结构转化为json
function treeToJ(tree){
let arr = []
return function getList(tree){
tree.forEach(item=>{
arr.push({
id:item.id,
pid:item.pid
})
if(item.children && Array.isArray(item.children)){
return getList(item.children)
}
})
return arr
}(tree)
}
json转树
function getTree(obj){
let tree = []
let objClone = {}
obj.forEach(item=>{
objClone[item.id] = item
})
console.log(objClone)
obj.forEach(item=>{
if(!item.pid){
tree.push(item)
} else {
objClone[item.pid].children || (objClone[item.pid].children = []).push(item)
}
console.log(item)
})
return tree
}
节流防抖
function throttle(fn,wait=300){
var timer = null
return function(){
let ctx = this
let arg =[...arguments]
if(timer)return
timer = setTimeout(function(){
fn.apply(ctx,arg)
timer = null
})
}
}
function debounce(){
var timer = null
return function(){
let ctx = this
let arg =[...arguments]
if(timer){
clearTimeout(timer)
return;
}
timer = setTimeout(function(){
fn.apply(ctx,arg)
timer = null
})
}
}
返回任意顺序
function shuffle(arr){
let m = arr.length, t,i
while(m){
i = Math.floor(Math.random() * m--)
console.log(i)
t = arr[m]
arr[m] = arr[i];
arr[i] = t;
}
return arr
}
大厂面试总结：www.jianshu.com/p/796a6e132… 常用的算法：www.conardli.top/docs/dataSt… 有一个面试：mp.weixin.qq.com/s?__biz=MzA… 大厂：mp.weixin.qq.com/s?__biz=MzA…
